This custom CSS should do it:
.main-navigation a:hover,
.main-navigation ul > :hover > a,
.main-navigation ul > .focus > a {
color: #bb00bb;
}
Don’t edit the theme files directly, otherwise your changes will be overwritten every time the theme is updated to the latest version.
An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.
As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.
If you’d like to learn more about CSS, here are a few resources to start you off:
https://dailypost.wordpress.com/2013/07/25/css-selectors/
https://dailypost.wordpress.com/2013/06/21/css-intro/
https://dailypost.wordpress.com/2013/08/29/css-matched-rule-pane/
https://en.support.wordpress.com/custom-design/how-to-find-your-themes-css/
https://thewc.co/articles/view/web-inspector-tutorial
https://htmldog.com/guides/css
